The invention relates to a power tool in which the tool performs a rotary motion. The invention thus refers generally to power tools such as, for example, power drills, screwing devices, power sanders, saws, and other machines of this kind.
There basically exists with power tools of this kind the problem of transferring sufficient torque to the tool, while at the same time the input drive power is to be minimized.
With hand-held power tools there results in this connection the additional problem that the reaction torque of the power tool must be absorbed by the user, which is why in manual operation in many cases even an increase in input drive power does not make it possible to transfer a greater torque to the tool, since the hand-held power tool can no longer be held by the user. This limits the diameter, for example, when drilling core removal holes in stone or metal.
With power drills, attempts have already been made to get around the problem of reaction torque by using an electropneumatic impact mechanism on the principle of the hammer drill, which essentially achieves "shattering" of the stone being drilled. A principle of this kind is not, however, usable for core removal drilling in stone or metal.
To achieve a high tightening torque in screwing devices, pulse screwing devices or impact screwing devices, with which high torques of several hundred Nm can be achieved, are used.
But even here, relatively high reaction torques for the user are produced. In addition, the stress on the screws and nuts caused by the impact pulse can lead to damage. Lastly, pulse screwing devices of this kind are suitable only for very high torques, and do not allow any fine adjustment of a predefined torque.
U.S. Pat. No. 2,392,097 discloses a power drill with reversible rotation direction in which a ratchet drive mechanism is used to generate a back-and-forth rotary motion that can be converted, by means of a claw that snaps into place alternatively in one or the other rotation direction, into a rotary motion to drive the tool in one rotation direction or in an opposite rotation direction.
A ratchet drive mechanism of this kind that interacts with a snap-in claw is, however, usable only for extremely low drive speeds, generates a high noise level, and possesses a relatively low efficiency. Moreover the life of the ratchet drive mechanism is relatively limited.
It is therefore the object of the invention to create a power tool that is as universally usable as possible, and with which a high torque at the tool can be achieved with a relatively low input drive power.
A further object of the invention consists in creating a power tool that is suitable even for high rotation speeds, and generates relatively little noise.
An additional object of the invention consists in creating a hand-held power tool that has a high torque transfer with low reaction torque and good efficiency.
A further object of the invention consists in creating a screwing device that allows a high torque and that, even when the screwing device is held with only one hand, has a low reaction torque such as to permit working with little fatigue.
Also to be created in this connection is a screwing device that allows presetting of a torque which, when reached, causes torque transfer to be interrupted.
Shutoff is to be as reproducible as possible, and shall allow operation with as little noise as possible.
Also to be created is a power tool with a high torque even at relatively low input drive power, which is advantageously usable as a power drill, power sander, saw, or sheet-metal cutter.